The present invention relates to an internal combustion engine, and specifically to an electronically controlled engine equipped with a controlling system for controlling an ignition timing in a changeover of a combustion condition of an engine from one combustion mode to another.
Japanese Patent Provisional (Kokai) Publication No. 62(1987)-110536 shows a conventional engine control system arranged to determine a target engine torque in accordance with one or more engine operating conditions such as accelerator depression degree and engine speed, and to achieve the target torque by controlling a throttle opening with an electronically controlled throttle valve.
Japanese Patent Provisional (Kokai) Publication No. 5(1993)-71381 shows another conventional engine control system arranged to hold the torque constant or vary the torque smoothly in a changeover between lean air fuel ratio and stoichiometric air fuel ratio or between stratified combustion and homogeneous combustion. This system varies the air fuel ratio gradually to prevent an abrupt torque change due to stepwise changes in a target air fuel ratio and a target cylinder intake air quantity.